商丹盆地丹江一级阶地黄土古土壤剖面碳酸钙含量研究

Study on CaCO_(3) Content in Loess Paleosol Profile of the First Terrace of the Danjiang River in Shangdan Basin

商丹盆地丹江一级阶地上广泛发育黄土与古土壤沉积物。通过野外地质考察,在商州紫荆村(ZJC)、乐园村(LYC)和丹凤茶坊村(CFC)3个典型黄土-古土壤剖面采集样品271个,实验室内利用气量法获得了样品CaCO_(3)质量分数。结果表明:(1)ZJC剖面CaCO_(3)质量分数介于0.145%~11.237%之间,LYC剖面CaCO_(3)质量分数介于0.067%~4.079%之间,CFC剖面介于0.067%~1.797%之间,各剖面平均值呈现ZJC>LYC>CFC。(2)综合剖面显示各地层单元的CaCO_(3)含量呈现MS>L0>S0>L1>T1-al,55000 a B.P.以来,商丹盆地经历了一级阶地洪水侵没(T1-al)→冬季风活动强烈气候干冷(L1)→夏季风增加气温升高降水增加(S0)→冬季风主导干旱少雨(L0)。(3)L0和S0区域对比显示,CaCO_(3)质量分数在空间呈现商丹盆地<关中盆地<宁夏长城塬,说明全新世时期与现代气候存在相似的空间分布特征,黄土风化程度呈现由东南向西北递减的趋势。

Typical loess and paleosol deposits are developed on the Danjiang first terrace in the Shangdan Basin.Through filed geological surveys,271 samples were collected from 3 typical loess-paleosol profiles in Zijing village(ZJC),Leyuan village(LYC)in Shangzhou district and Chafang village(CFC)in Danfeng county in Shangluo city,Shaanxi province.In the laboratory,the data of CaCO_(3) content in loess paleosol samples were obtained by the gas method.The results show that:(1)The content of CaCO_(3) in the ZJC profile is between 0.145%and 11.237%,while the LYC profile is between 0.067%and 4.079%,the CFC profile is between 0.067%and 1.797%.The average value of each profile is ZJC>LYC>CFC.(2)The comprehensive profile shows that the CaCO_(3) content of each strata unit is MS>L0>S0>L1>T1-al.Since 55000 a B.P.,the Shangdan Basin has experienced the first terrace flood intrusion(T1-al)→Winter monsoon strong activity and the climate is dry and cold(L1)→Summer monsoon increase,temperature rises and precipitation increase(S0)→Winter monsoon dominates drought and less precipitation(L0).(3)The region comparison of L0 and S0 shows that the content of CaCO_(3) spatially presents the Shangdan Basin<Guanzhong Basin<Ningxia Changcheng Plateau,indicating that the Holocene and modern climate have similar spatial distribution characteristics,and the degree of weathering of loess is decreasing from southeast to northwest.